Achieving the most uniform temperature on the surface of a heater can be limited due to the thermal conductivity of the materials of construction. Often, material options are limited by factors such as temperature rating, chemical compatibility, or thermal expansion. Geometry of the heater can have a significant impact on asymmetric losses and aggravate thermal non-uniformity. Typically, experience and thermal modeling are used for the heater design for the most effective power distribution. Heat homogenizing ceramic materials may be used for the outer plates. Metallic heat spreaders, e.g., a copper core, may be used. But, even with the most effective heater layout and construction, the thermal uniformity may need still further improvement, as a typical heating plate at 250° C. may have a maximum-minimum range of as much as 15-20° C. Examples of prior heaters are provided in U.S. Pat. No. 4,481,406 (Muka), U.S. Pat. No. 6,534,751 (Uchiyama et al.), U.S. Pat. No. 6,758,263 (Krassowski et al.) and U.S. Patent Application Publication No. 2009/0235866 (Kataigi et al.).